The present invention relates to catalytic converters, and more particularly, to a method and apparatus for the removal of excess coating material from a catalytic converter honeycomb body which is capable of having fluid flow through it and which exhibits flow channels. The general flow direction of the flow channels is defined by the longitudinal axis of the honeycomb body and the honeycomb body has an axial length and a center of gravity. The honeycomb body is surface coated and is then rotated around a first rotational axis with a first rotational frequency in the direction of the longitudinal axis. The distance between the center of gravity of the honeycomb body and the rotational axis is at least 1.5 times the axial length of the honeycomb body.
A catalytic converter support body generally includes a honeycomb body having a large enough surface to exchange exhaust fumes flowing through the support body with high efficiency. As shown in FIG. 1, a honeycomb body 2 includes a plurality of flow channels 17 formed of wrapped or layered metal foils 4 that are located between bordering layers 3. The flow channels 17 define the longitudinal axis of the honeycomb body 5. The honeycomb body 2 is preferably made from rust resistant and high temperature resistant steel.
Even though the flow channels 17 of the honeycomb body 2 preferably have a large enough surface area to exchange harmful fumes, it is known in the art to coat the flow channels 17 of the honeycomb body 2 with a coating material 1. Such coating materials may include gamma-aluminum oxide or washcoat made from oxides. These coatings are catalytically active or are necessary coating materials for machines. Specifically, the coating material lifts catalysts such as platinum or rhodium, and thereby causes a further mixing of the exhaust fumes which flow through the honeycomb body 2 because of the extremely intensive contact of the catalysts with the exhaust fumes. Normally, the honeycomb body 2 is submerged into a bath of emulsified coating material or sprayed with such material so that the complete surface of the honeycomb body is coated. Afterwards, the excess coating material is removed from the surface by means of compressed air, especially from the flow channels 17. This procedure for removing the excess coating material is suitable if the flow channel 17 cross section is large enough and if the coating thickness is relatively thick because in such a case, the surface tension of the capillary force is of no significance.
However, in order to enlarge the surface of the catalyst to increase catalytic conversion efficiency, it is necessary to further increase the density of the flow channels 17. Until recently, cell densities of less than 600 cpsi (cells per square inch) were usual, but the goal now is to reach a cell density of 1000 or more cpsi. With higher cell densities, smaller flow channel 17 cross-sections exist, so the influence of the surface tension and the capillary power increases. This causes drops of the coating material 1 to fall into the flow channels 17, which leads to a coating surface having varied thickness 19 and sometimes clogs and damages the flow channel 17, as shown in FIG. 2. Thus, the varying thickness D of the coating is a significant problem associated with increasing cell densities in honeycomb bodies 2.
Accordingly, there is a need in the art for a method of removing excess coating material from honeycomb bodies having increased cell densities and small flow channels to provide a uniform application of the coating material. There is a further need for an apparatus suitable for performing such a procedure.